With spreading of Liquid Crystal Display (LCD), more attentions have been drawn to LCD, especially the Thin Film Transistor-Liquid Crystal Display (TFT-LCD), and requirement to the quality of picture thereof is growing. Thus, manufactures producing the TFT-LCDs are required to perform restrict parameter tests on the TFT-LCD panels to ensure the quality of products.
Existing tests of TFT-LCD panels are realized by input a variable electric signal to a signal input of the TFT-LCD panels so as to obtain different examination pictures. However, TFT-LCD is a passive display device which will not radiate light by itself. It realizes the image display by using the electro-optical effect of the liquid crystal and controlling the light intension of displaying part through an alternative electric field, thus an important premise for carrying out tests of TFT-LCD panels is to have a backlight source for providing a constant luminance for the tests, so that stable gray scale can be ensured in the tested picture. Bad detection rate of TFT-LCD panels also depends on the stability of luminance of the backlight source directly. If abnormality occurs in the backlight source which decreases or increases the luminance in testing, it is hard to be recognized by human eyes, and has to be measured by specific testing instruments and then be adjusted manually, which is time-consuming, and there are errors in the manual adjustment.